The overall objective of this research is an assessment of damage produced by light generated temperature increase in the eye. One form of damage is the formation of a visible lesion in the ocular fundus. Another form is the actual loss of functional vision. Our current objective is the measurement of the critical temperature histories associated with the formation of minimum visible damage and the comparison of these histories to a computer solution to the heat conduction equation for the fundus. Measurements will be made with microthermocouples 10-20 micron A seconds to 5 minutes. The effect of laser retinal irradiation on functional vision will be measured as a change in neuronal activity of the LGN. A visual stimulus will be presented to an immobilized cat before and after laser irradiation. The neuronal response will be recorded with a micro electrode in the LGN.